My 2nd top chop on a model A, first went well on my coupe. My "30" sedan didn't. After cutting roof, "B" post on left came forward against door. Right side stayed in place. Body was bolted to frame, doors and everything was lined up prior to cutting. Had braces between "B" post and cowl. Nothing toward the back which probably caused the problem? "A" post or cowl didn't move. Would appreciate input on how to tackle this problem.